Shielded spark plug



April 30, 1940. E. s. TWINING ET AL SHIELDED SPARK PLUG Original FiledMay 8, 1959 Patented Apr. 30, 1940 PATENT OFFICE SHIELD-ED Earl S.Twining and SPARK PLUG Brace H. Sibley, Toledo,

Ohio, assignors to Champion Spark Plug Company, Toledo, Ohio, acorporation of Delaware Application May 8, 1939, Serial No. 272,340Renewed August 10, 1939 Claims.

This invention relates to radio shielded spark plugs and particularly tothe assembly of plugs of this character. The invention has for itsprimary object the provision of an inexpensive 5 spark plug which willeffectively ground emanations from the ignition system having a tendencyto interfere with radio reception in automobiles and aircraft.

Spark plugs having the desired radio shielding characteristics haveheretofore been quite expensive for the reason that the materials whichentered into their construction were costly and could be assembled onlywith difliculty. The exception to this was in plugs of the so-called cantype in which a shield was fixed over a standard spark plug. Adisadvantage of this type, however, was in the fact that the heatdistribution of the spark plug was upset by the shield so that the plugsran hotter than usual and occasionally beyond the range for which theywere designed.

The present invention includes a spark plug having a separate shieldbarrel which is made functionally integral with the plug in assembly andwhich overlies a body of compacted powder or other insulating materialof excellent heat conduction characteristics, the barrel being held inplace merely by rolling in a portion of the adjacent spark plug shell.By this construction an inexpensive and highly eflicient shielded sparkplug is provided which may be constructed of materials of relatively lowcost.

Further objects and advantages of the invention will become apparentfrom the following 5 specification, reference being had to theaccompanying drawing, in which:

Figure 1 is a center vertical section, with'the electrodes in full, ofan assembled spark plug in accordance with the present invention;

Fig. 2 is a composite view of the parts prior to the last assemblingoperation, and

Fig. 3 is a fragmentary sectional view of a modified form of theinvention.

Referring to the drawing, the spark plug ineludes the usual metallicshell'5 which carries a ground electrode 6. A ceramic insulating body Iis held within the shell by a body of compacted powder 8 and in turnsupports the center electrode 9. The parts so far described mayadvantageously be assembled in accordance with the disclosure of DewarPatent No. 2,072,087, dated March 2, 1937.

Instead of forming a shielding barrel and the spark plug shell from asingle piece of material, which forming operation is accomplished byconsiderable Waste, the present invention provides a separate shieldingbarrel Ill which may be of any suitable material similar to or difierentfrom the material of the shell 5. In the preferred embodiment of theinvention, the barrel I0 is upset at one end as at H to provide anangular shoulder I2, and is threaded at its upper end as at 13 for thereception of the usual harness.

The body of compacted powder 8 is made to stand at a predeterminedheight in the interior of the shell 5 and, in assembly, a gasket M ofcopper or other material having a very high heat conductivity, is placedimmediately over a compacted powder. The barrel I0 is then inserted overthe gasket in the shell 5 and an upwardly extending tapered flange I5 isrolled in over the shoulder I2 of the barrel to hold the latter tightlyin place in electrical contact with the shell and in heat transferrelationship with the gasket M.

An insulating sleeve I6 is subsequently introduced into the barrel Illeither alone or as a part of the harness which carries the usualignition cable IS. The sleeve I6 is sufiiciently long so that it entersthe barrel well beyond the end of the center electrode 9. The dielectricpath between the upper end of the center electrode and the nearestadjacent exposed portion of the barrel I0 is thus sufliciently long toprevent arcing between these two surfaces.

In the modification shown in Fig. 3, the shield barrel includes anextension Ill received in threaded engagement with a bushing 20, whichlatter is fastened into the shell in the same manner as the shieldbarrel ll! of the form previously described. This ,construction providesa twopiece shield barrel which may be made of inexpensive materials andwhich is adapted for assembly on the Dewar machine so that the shell andcenter assembly parts are standard. If desired, the barrel Ill may belined with insulating material, or a separate insulating sleeve similarto the sleeve 16 may be inserted within the barrel.

What we claim as new and desire to secure by United States LettersPatent is:

1. A spark plug of the class described includ ing a spark plug shellhaving an initially open upper end, a bodyof compacted insulating andholding material disposed within said shell to a predetermined height,and a separate shield barrel inserted within said shell in heat transferrelationship both with said shell and with the compacted insulating andholding material.

2. A spark plug of the class described including a spark plug shellhaving an initially open upper end, a bodyof compacted insulating andholding material disposed within said shell to a predetermined height, aseparate shield barrel in-'- serted within said shell, a shoulder onsaid shield barrel and an inturned extension on said shell in contactwith said shoulder whereby said shield barrel is held in electricalcontact and heat transfer relationship with said shell and saidcompacted insulating and holding material.

3. A spark plug of the class described including a spark plug shellhaving an initially open upper end, a body of compacted insulating andholding material disposed within said shell -to a predetermined height,and a separate shield barrel having a portion inserted within said shellin heat transfer relationship both with said shell and with thecompacted insulating and holding material.

4. A spark plug of the class described including a spark plug shellhaving an initially open upper end, a body of compacted insulating andholding material disposed within said shell to a predetermined height,and a separate shield barrel including a threaded bushing insertedwithin said shell in heat transfer relationship with said shell and withthe compacted insulating and holding material, and an extension threadedon to the outer end of said bushing.

5. A spark plug of the class described including a spark plug shellhaving an initially open EARL S. TVVINING. BRACE H. SIBLEY.

